Alum Priming Salt


In the Kreidezeit range, Alum Priming Salt is used as a barrier primer against visible discolouration and stains from old substrates: Water edges, discolouration from paste residues, etc.

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Alum – or potassium aluminium sulphate – is a salt which is rather insoluble in cold water and soluble in warm water. It is used, among other things, as a hemostatic agent in razor pins, as a deodorant crystal, as a fixing aid in plant dyeing, as a primer in distemper painting.

In our range of products, Alum Priming Salt is used as a barrier primer against penetrating discolorations and stains from old substrates: Water marks, discolorations from paste residues, etc.
The best results are achieved when applied to new KREIDEZEIT Lime Plasters or new KREIDEZEIT Lime Paints.

The blocking effect of alum is based on a reaction with lime that has not yet set, on the closure of the capillaries of plasters by recrystallization and on its poor solubility in cold water. The faster the next coat dries, the greater the chance of success. On old plasters, alum does not have a significant blocking effect. As a rule, alum does not help against nicotine discoloration.

The lime plasters and lime paints should be treated with alum shortly after drying, the blocking effect is better if the lime has not yet been carbonated.
Then coat with KREIDEZEIT Lime Paints or apply thin layers of KREIDEZEIT Lime Wall Finishes (max. thickness 1-2 mm). After treatment with KREIDEZEIT Casein Primer, can also be painted over with KREIDEZEIT Vega Wallpaint, Clay Paints, or Distemper. Can not be coated with GekkkoSOL paints.

It is not recommended to coat the primed surfaces with thick layers of plasters, the drying time might be too long and the moisture could dissolve the alum and the dyes again.

In contrast to commercially available and usually solvent-based and vapour-tight sealing bases, alum has only a minor effect on the vapour absorption of the substrate.
The success of the application cannot be guaranteed. However, the chances of success are so high that an attempt is worthwhile and depends directly on professional processing.
Before carrying out large-area work, it is recommended that test areas be laid out to check the effectiveness of the alum.



  • Salt for mixing with water
  • blocking
  • vapour-permeable
  • solvent-free and emission-free, odourless
  • absorbency reducing
  • hardening
  • acidic, pH 3-3.5 at 10% solution
  • slightly disinfecting
  • vegan


Full Declaration

100 % potassium aluminium sulphate x 12 H2O

When using the product, the complete Productinformation Alum Priming Salt must be observed.

Preparing the Alum Solution
Dissolve the priming salt in warm water while stirring (duration: approx. 5 min.). The warmer the water, the more salt dissolves. A sediment of salt crystals is normal and indicates that the solution is saturated. Do not process the sediment.

Water demand
Dissolve approx. 100 g of alum primer in 1 litre of water.

Substrate requirements
The surfaces must be completely dry and absorbent!


  1. Allow new lime plaster or lime paint to dry out completely.
  2. Apply alum solution until the substrate is saturated (paint or spray, do not roll!). Application temperature min. 8°C.
  3. Allow to dry out completely.
  4. Sweep off excess alum (salt crystals).
  5. Coat with KREIDEZEIT Lime Paint, Lime Wall Finish or another suitable KREIDEZEIT wall paint. Ensure rapid drying.

Drying Time
Dry and coatable after 24 hours at the earliest, depending on room climate conditions.

Suitable Tools
Facade and ceiling brushes. Do not spray or apply with a roller.

Cleaning the Tools
Immediately after use with water.

Productinformation Alum Priming Salt

Material Safety Data Sheet Alum Priming Salt

A typical example from practice
When renovating a room, the old wallpaper was removed. The paste residues on the walls were not or not sufficiently removed. In order to level out the structure, the old substrate was completely covered with lime adhesive plaster. After drying, there is a full-area yellowing or only individual yellow clouds. This is yellowing dye from the old paste, and it will continue to stain in every subsequent coat. Now treat with alum and then coat with a wall paint and the yellowing agents will not dye again.
The wall was renovated in a natural, non-toxic and vapour-open manner.

Product reacts slightly acidic. Avoid splashes and coatings on adjacent components, or remove them immediately and / or protect adjacent components accordingly. Product may damage or discolour acid-sensitive surfaces (e. g. marble, soapstone).

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